[Greenbuilding] is it ever sensible to use PV to heat water?

[Steven Tjiang]

Reuben, why are virtues of banking deceptive?
I understand the grid issues but in my opinion, we are no where near having
enough PV to have those problems.  when we get there.....that's a good
problem to have (and solve).

---- Steve (KZ6LSD)


On Fri, Mar 23, 2012 at 11:30 AM, Steven Tjiang <steve at tjiang.org> wrote:

> Reuben
>
> You use the excess PV generation from the summer to heat the water in the
> winter.  It's not economical to oversize a solar thermal system.
>
> I still about 50% of my summer PV output in the winter.  But SF bay area
> is more sunny than NW.
>
> ---- Steve (KZ6LSD)
>
>
>
> On Fri, Mar 23, 2012 at 11:28 AM, Steven Tjiang <steve at tjiang.org> wrote:
>
>> +1 for simplicity
>>
>> I located our heat pump water heaters in my unheated workspace.  I have
>> several months of temperature measurements down there.  It has never gone
>> below 55F in the winter. I know other climates may not be so lucky.
>> I use solar preheat with an ICS (Sun Earth Copperheart).  There are no
>> pumps, just a few valves.  The water heater is effectively off all summer.
>>
>> Having said that I'd have to say that DIY may make an active solar
>> thermal system worthwhile but let's face it....this is not what most people
>> do.
>>
>> ---- Steve (KZ6LSD)
>>
>>
>>
>> On Fri, Mar 23, 2012 at 11:13 AM, Michael O'Brien <obrien at hevanet.com>wrote:
>>
>>> Hi, Steve--
>>>
>>> First of all, I want to validate your decision. Since we are in a time
>>> of rapid innovation and change, it's important that people try different
>>> solutions and keep the rest of us informed about their experience and
>>> outcomes. It's too soon to conclude that one solution is the best for every
>>> need.
>>>
>>> Charlie Stephens is a good friend and I respect his opinions. However,
>>> in his enthusiasm for bleeding edge innovation, he is sometimes wrong. He
>>> is fearless when it comes to complexity, for example, and will recommend
>>> solutions that only highly specialized technicans can install or maintain.
>>> I'd suggest listening carefully to his recommendations and do your own due
>>> diligence. He speaks forcefully so it's easy to think he must be right.
>>>
>>> Here in Oregon there have been thousands of solar hot water systems
>>> installed on homes, and they are generally reliable and trouble-free. We
>>> have one on our house that is five years old and works fine. The net
>>> installed cost to us was under $2000, so the payback is about 8 to 10 years.
>>>
>>> An air-to-water heat pump sounds good in terms of efficiency, but
>>> consider: most models draw heat out of the ambient air where the heat
>>> pump/tank combo is located, which is usually inside the house. If the house
>>> is in a heating climate, the heat pump is going to take heat out of
>>> conditioned air. That means the heat pump will also cool the house during
>>> the heating season, which is counter-productive. This idea makes sense for
>>> a split system like the Daikin Altherma with an outdoor unit, but the cost
>>> estimate was $22,000 for our house. Granted it has a COP of around 4, but
>>> even running it on low-cost PV, that's a big investment and there are  as
>>> yet no financial incentives or tax breaks.
>>>
>>> I believe simplicity and reliability are essential to long-term energy
>>> savings and reduced costs. If equipment has high efficiency but you can't
>>> find anyone who knows how to maintain or repair it, the initial savings can
>>> be eaten up quickly. Not to mention the hassle factor.
>>>
>>> Best,
>>>
>>>  Mike O'Brien
>>>
>>>
>>>
>>>
>>> On Mar 23, 2012, at 9:50 AM, molasses at q.com wrote:
>>>
>>> On this topic:
>>> http://www.greenbuildingadvisor.com/blogs/dept/musings/solar-thermal-dead
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>>
>>
>
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